If you have your head in the skin care game, you’ve likely heard of vitamin C serums.

Vitamin C is touted as one of the best anti-aging ingredients on the market — and the key to maintaining a smooth, even, and glowy complexion.

Although you’re probably getting vitamin C in your diet, there’s no way to guarantee that it’s going straight to your skin. Using serums and other topical products is the most direct way to reap these benefits.

Read on to learn why you should add vitamin C serum to your routine, how to introduce a new product, and more.

Magnesium ascorbyl phosphate, one of the main vitamin C derivatives used in skin care, has been shown to have a hydrating effect on skin. It decreases transepidermal water loss, allowing your skin to better retain moisture.

Sun damage is caused by molecules called free radicals. These are atoms with a missing electron. Free radicals search for other atoms from which they can “steal” an electron —and this can lead to significant damage to the skin.

Although topical vitamin C is generally well-tolerated, all skin products have the potential to cause side effects. You should always do a patch test to assess your risk for allergic reaction. Here’s how:

Select a small area of skin that’s easy to conceal, like your forearm.

Apply a small amount of product and wait 24 hours.

If no side effects occur, you can apply to your face. Discontinue use if you develop a rash, redness, or hives.

When it’s time for a full application, follow the instructions on the product’s label.

Vitamin C serum is typically applied once or twice per day. A good rule of thumb is to cleanse, tone, apply vitamin C serum, and then moisturize.

It can be safely used in conjunction with other active ingredients, although use alongside niacinamide may render vitamin C less effective.

Make sure to check your product’s use-by date. If the product has darkened or otherwise changed color, the vitamin C has likely oxidized. Although the product is still safe to use, it no longer carries the same benefits.

Consistency is key for maximum effect, so add it to your routine in a way that makes sense for you. Some people apply it in the morning to take advantage of its UV-protectant properties, while others find that it works best as a night serum.

Discontinue use if you begin to experience irritation or discomfort.

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